1. Field of the Invention
This invention lies in the field of electrical logging apparatus. More specifically, it concerns electrical logging apparatus for use in deep boreholes wherein the signals generated by the instrument in relation to the earth parameters to be measured, are stored at selected intervals of time in a digital solid state memory.
When the series of measurements are completed the logging sonde is brought to the surface and the digital data stored in the memory is retrieved, converted to analog values and displayed or recorded for later processing.
2. Description of the Prior Art
In the prior art, logging measurements which were made by assembling an instrument, sensitive to a parameter of the earth, such as pressure or temperature, for example, placing it in a sealed capsule, and lowering it to a selected position in the borehole and left for a period of a selected number of hours or days. Such instruments have always been designed with analog recording means within the capsule, and generally use a sharp pointed stylus in contact with a metal sheet or chart, such that the stylus responsive to a sensor, sensitive to pressure or temperature, moves across the metal sheet, in one coordinate direction, while clock mechanism moves the metal sheet in a second coordinate direction.
Because of the limited size of such borehole instruments, the area, or coordinate dimensions, of the recording sheet or chart are so small that it becomes impossible to measure changes in the earth parameter smaller than some minimum value. There appears to be no way of making the stylus point sharper or the recording chart larger to improve this situation.
It becomes an important object of this invention, therefore, to provide a subsurface logging instrument which is self-contained, in which the earth parameter is converted to an electrical signal which is digitized and stored in a digital storage memory, so that when the instrument is brought to the surface, the successive values of the electrical signal which have been stored, can be retrieved electrically and displayed.
Alternately, the digitizing means can be installed at the surface, connected by conducting cable to the sensors in the sonde, to provide a continuously surface recording logging instrument.